Tire uniformity is important to overall performance. Non-uniformities may occur during the tire building process, green tire storage, or during loading and shaping of the green tire into the tire press prior to curing. One aspect of tire non-uniformity is when the opposed tire beads are not concentric and parallel to each other. As shown in FIG. 1, a prior art green tire loader grasps the tire from the top bead and positions the lower bead onto a bottom mold bead ring in the press. Next, the top bead is released without control of its location relative to the bottom bead, or the top mold bead ring. One problem with the prior art loader is that the lower sidewall bead region has not been rotated into cured position prior to engagement with the tapered bottom bead ring, and the loader is incapable of improving this undesirable condition. A second problem is that the green tire may or may not be centered on the loader or the bottom bead ring in the mold. A third problem is that the prior art tire loader has no means to accurately hold the top bead of the green tire concentric or parallel to the bottom bead.
FIG. 2a illustrates a green tire having a bead seated on the bottom mold bead ring 12 prior to shaping and with the mold in the open position. At this point, dimension X is equal to dimension Y. As shown, the lower sidewall bead region 14a is constrained by the bottom mold bead ring 12, while the top sidewall bead region 14b is unconstrained. FIG. 2b illustrates the green tire during shaping of the curing bladder. FIG. 2b also illustrates that the lower ply endings A near the bottom mold bead ring are trapped between the bladder and the tapered bottom mold bead ring, thus severely restricting the lower sidewall area from rotating into the proper position. During bladder shaping the mold is not closed allowing the upper bead area to be unrestrained. As the shaping pressure increases, the upper ply endings B are pulled back around the bead resulting in an increase in the Y dimension. The increase in the Y dimension also causes the centerline of the tire to shift laterally from the desired centerline a distance L, further causing conicity. Thus as shown in FIG. 2b, dimension Y is greater than X resulting in tire non-uniformity. When the press closes, the top mold bead ring engages the top bead, and forces the material in the top bead area to rotate around the top bead. The non-uniformity of material rotation around the top bead is similar to that of the bottom bead. Closing of the curing press does not solve the issues described above, and a tire with non-uniformity issues may still be cured.
It is thus desired to provide an improved apparatus for preforming the green tire prior to entry into the mold to ensure that the tire beads are concentric and parallel to each other. It is further desired to provide an improved apparatus that ensures the top and bottom bead areas are rotated into the proper cured position prior to placement into the tire mold and when loaded into the mold.